Now the actual pressure and transport model classes are not specified,
but taken as template template parameters, also grid and well model
are templates for both the sequential model and the simulator class,
although at this point only StandardWells is expected to work with
the sequential model.
Instead of the WellsManager guessing which wells are handled by other
processes we now use tha ouput of the load balancer to compute wells
that are handled by other processes.
With the previous approach it was not possible to calculate this information
correctly. Wells with only one completion next to the border of the
processes' partition were represented on multiple processes. In additition
wells that the eclipse schedule section defined with completions on non-active
cells in sequential runs were not at all calculated in parallel runs.
With the new approach the CpGrid::loaBalance routine returns the set names of
wells that are not handled by this process when setting up the simulation. This
information is then used throughout the simulation.
This commit adds sequential solvers, including a simulator variant
using them (flow_sequential.cpp) with an integration test (running
SPE1, same as for fully implicit).
The sequential code is capable of running several (but not all) test
cases without tuning or special parameters, but reducing ds_max a bit
(from default 0.2 to say 0.1) helps with transport solver
convergence. The Norne model runs fine (esp. with a little tuning). A
parameter iterate_to_fully_implicit (defaults to false) is available,
when set the simulator will iterate with alternating pressure and
transport solves towards the fully implicit solution. Although that
takes a lot extra time it serves as a correctness check.
Performance is not competitive with fully implicit at this point:
essentially both the pressure and transport models inherit the fully
implicit model and do a lot of double (or triple) work. The point has
been to establish a proof of concept and baseline for further
experiments, without disturbing the base model too much (or at all, if
possible).
Changes to existing code has been minimized by merging most such
changes as smaller PRs already, the only remaining such change is to
NewtonIterationBlackoilInterleaved. Admittedly, that code (to solve
the pressure system with AMG) is not ideal because it duplicates
similar code in CPRPreconditioner.hpp and is not parallel. I propose
to address this later by refactoring the "solve elliptic system" code
from CPRPreconditioner into a separate class that can be used also
from here
